The invention is concerned with a three-dimensional combined magneto-optical memory and logic processor which comprises a plurality of parallel sheets (layers) of magnetic bubble material, such as an ortho-ferrite garnet, or an amorphous substance. For example, each layer comprise a single crystal bismuth substituted iron garnet film grown on a non-magnetic substrate. These layers are transparent to light, electromagnetic beams or lasers. Each layer has an array of two-dimensional electrical addressable pixels, or magnetic bubbles, which affects the polarization state of light transmitted through the particular layer. A multiplicity of such layers are placed parallel to one another to form the three-dimensional combined memory and logic processor of the invention.
As described in U.S. Pat. No. 4,660,173, which issued Apr. 21, 1987, in the name of the present inventor the three-dimensional magneto-optic memory operates by passing vertically polarized light through each layer and through each pixel (magnetic bubble) in the array formed on each layer. This causes a polaroid light to exhibit a large magneto-rotation effect by which the plane of polarization for linearly polarized light transmitted by each bubble is rotated, either clockwise or counter-clockwise depending on the magnetization of the bubble. The rotation angle is d: where: d is the thickness of the material, and is the Faraday rotation co-efficient.
In order to analyze the polarization state of the light transmitted through the layers, the light from the memory is passed through an analyzer polarizer. This polarizer may be oriented to block the light which passes through the one of magnetic bubbles, but to pass the light which does not pass through a magnetic bubble. The magnetic bubbles may be established on each layer in desired patterns which are programmable by an external data processing system. The patterns may be major loop or minor loop bubble systems, T-bar angel fish, cross-conduction channels, or any other suitable type of known configuration. Biased magnetic fields may be used to establish the magnetic bubbles on each layer in the desired pattern under the control of the external data processing system.
In the system to be described, the magnetic bubbles on each layer represent either binary data stored in the device or logic functions. The presence or absence of a magnetic bubble, or an incomplete bubble, at any particular location on each layer indicates binary 1 or 0 or -1. The electro-magnetic (laser) beam passing through each layer and indicating different bubble combinations, such as 0-1-0 may indicate data or logic functions, as the three-dimensional processor of the invention performs a dual function of a memory and also as a logic processor. Logic functions similar to "and", "or", "nor", or mathematical operations may be programmed on each layer.
To reiterate, each layer of the three-dimensional system to be described has the property that when subjected to a particularly biasing magnetic field directed perpendicular to the surface, small bubble domains are formed with polarization oppositely directed to that of the rest of the material of the layer. Local magnetic fields applied to the layer can be used to generate or annihilate the magnetic bubbles, as explained above. For example, conductive loops may be placed on the surface to generate magnetic fields, which drive the bubbles in particular directions. A property of the ortho ferrite magnetic bubble domain materials is that the polarization of light passing through the bubbles is altered in a manner different from that of the light passing through the remainder of the material because of the occurrence of magneto-optic rotation and change in wavelength. The polarization effects are similar to the polarization effects encountered in a magnetic hologram as described in an article in the IEEE Transactions on Magnetics, Vol MAG-6, No. 3 September 1970, by Haim Haskal entitled "Polarization and Efficiency in Magnetic Holography".
As described in the article, a laser beam E linearly polarized in the Y plane, for example, is rotated by a magnetic hologram via the Faraday or Kerr effect. When such a beam E is passed through a magnetic bubble, the polarization of the beam as it passes through the bubble is rotated by an angle F; where F is the specific Faraday rotation in degrees/centimeter, and t is the thickness of the magnetic film forming the bubble.